Growth pattern of ‘Búlida’ apricot trees in Mediterranean conditions A. Pérez-Pastor a,c, A. Torrecillas b,c, P.A. Nortes a, J.P. Pérez-Abellán a, R. Domingo a,c, Mª C. Ruiz-Sánchez b,c a Dpto. Producción Vegetal, Universidad Politécnica de Cartagena (UPCT), Cartagena, Murcia, Spain b Dpto. Riego, Centro de Edafología y Biología Aplicada del Segura (CEBAS-CSIC), P.O.Box 164, Espinardo, Murcia, Spain c Unidad Asociada al CSIC de Horticultura Sostenible en Zonas Áridas (UPCT-CEBAS) Photograph 2. Phenological growth stages of Búlida apricot trees, according to BBCH (numbers) and Baggiolini (letters) codes Figure 1. A) Apricot fruit growth in diameter (mm) and fresh weight (g). B) Shoot and fruit growth, expressed as percentage of the maximum growth. Table II. Pheno-climatology for Búlida apricot. Predominant dates of growth stages, occurrence of BBCH codes, and growing degree hour (GDH) accumulated at the beginning of each stage.. 1.OBJECTIVE The aim of this paper was to define the phenological fruit stages of Búlida apricot trees, using BBCH code and GDH model. This information will improve the cultivation of this crop in Murcia Region (which produces 58 % of the total Spanish production) by expressing the timing of most agricultural operations on a standardised scale. 2. MATERIALS AND METHODS The experiment was conducted during two growing seasons (1997 and 1998) in a 2 ha plot of a commercial orchard, located in Mula valley, Murcia (SE Spain), with a loam texture soil. The climate was typically Mediterranean, with mild winter and dry summer (Table I). The plant material consisted of twelve-year-old apricot trees ( Prunus armeniaca L., cv. Búlida, on Real Fino apricot rootstock), spaced 8 x 8 m, with an average height of 4.5 m, ground cover of 52 % and leaf area index (LAI) of The shape of the trees resulted from an open-centre tree training-pruning system (Photograph 1). Trees were drip irrigated using one drip irrigation line for each row, with seven emitters per tree, each with a flow rate of 4 l h -1. BBCH Stage 7: Fruit development included 71 code: fruit set, corresponding to stage H of the Baggiolini code; 73: physiological fruit drop, starting at the beginning of April, with 9269 ºC GDH; 75: Fruits about 50 % of final size. Since harvest followed local commercial criteria, this phenological stage would correspond to something included in Stage 8: Fruit maturity: 89 BBCH code: Fruit ripe for consumption and showing full organoleptic characteristics. GDH accumulation for this cultural procedure occurred at an average of ºC GDH for the experimental period. Table I. Monthly maximum, minimum and mean air temperatures, relative humidity (HR), rainfall, mean daily evaporation rate (Epan), wind speed (2 m) and net radiation. Irrigation amounts were scheduled weekly based on crop coefficients (Abrisqueta et al., 1994), reference crop water use (ETo), as determined from data collected the previous week in a class A pan, and the estimated application efficiency (95 %). The water amounts applied for the control treatment averaged 7154 m 3 ha -1 year -1, maintaining the soil close to field capacity values in the main root zone. Trees were fertilised with 164 kg N, 60 kg P 2 O 5 and 118 kg K 2 O, per ha per year. A routine pesticide programme was maintained. No weeds were allowed to develop within the orchard, resulting in a clean orchard floor for the duration of the experiment. Harvest was carried out following local commercial criteria on several dates during one month, the first pick taking place in mid-May. The average yield for the studied period was 256 kg tree -1 (5300 fruits tree -1 ). The different phenological stages of apricot growth were defined according to the BBCH General Scale (Lancashire et al., 1991; Meier et al., 1994). To record the phenological stages, as well as the duration of every stage, four healthy trees were selected at random from control trees of each block. From each tree, four two- year-old branches (1 m long and 1.5 cm 2 in diameter, each containing bud flowers) for each compass direction, were tagged. Twice a week, from the end of January (dormant buds) to leaf fall in December the different phenological stages were recorded separately. From fruit-set to harvest, counting was only carried out once a week. The shoot length of four tagged shoots per tree, one from each compass direction, was measured on one tree per block every 14 days, while the trunk diameter in all control trees (five per block) was measured every two months, 30 cm above the soil line. The diameter of 10 tagged fruits per tree was measured weekly in all control trees per block using an electronic digital calliper. The influence of temperature on the duration of each phenological stage was studied using the growing degree hour (GDH) model (Richardson et al., 1975) calculating the GDH’s by subtracting 6ºC (base temperature according to Tabuenca and Herrero, 1966) from each hourly temperature.. Photograph 1. Apricot trees in field conditions Fruit growth, measured as fruit diameter, follows a double-sigmoide pattern (Fig.1A), with two periods of active growth, the first at the end of March and the second at the end of May, separated by the lag phase of slower growth and dominated by lignification of the endocarp. The first period occurred after the first shoot growth period and coincided with maximum root growth (data not shown). The second shoot growth period began during the second rapid fruit growth period. It is clear that both peaks of shoot growth occurred simultaneously with the lowest rate of fruit growth. Figure 1B shows data for shoot and fruit growth expressed as a percentage of maximum growth at harvest. It is clear that the first phase of rapid fruit growth started when around 85% of shoot growth was completed and the second phase of fruit growth initiated when the 100 % of shoot growth was completed. There was an additional stage of shoot growth, occurred after harvest (data not shown). The relative separation between shoot and fruit growth periods in apricot plants (Figure 1B) is essential for the successful application of regulated deficit irrigation strategies (Goldhamer, 1989), since indicates that deficit irrigation may be applied to control shoot growth without detrimental effects on fruit growth and yield. The separation between both processes was similar to that observed in other woody plants (Mitchell et al., 1984; Domingo et al, 1996; Goldhamer, 1989; Mitchell and Chalmers, 1982). 3. RESULTS AND DISCUSSION The phenological stages of Búlida apricot trees, according to the BBCH code is shown in Photograph II, as well as the growing degree hour (GDH) accumulated at the beginning of each stage are shown in Table II. The accumulation of GDH at full bloom (65 BBCH code, Stage 6: Flowering) was 3584 and 3983 ºC GDH in 1997 and 1998, respectively, which resulted in a Difference of three days between the respective full bloom (5 and 8 March). This stage corresponding to Baggiolini stage F (50 % of open flowers). This study was supported by a CICYT (HID ; AGL C05-04 and -05) grants to the authors.